1. Field of the Invention
This invention relates to novel improved dewaxing processes carried out in the presence of highly siliceous porous crystalline materials.
2. Description of the Related Art
It is known to treat gas oil fractions, i.e. petroleum fractions having an initial boiling point of at least about 330.degree. F., so as to selectively remove paraffinic hydrocarbons therefrom. This technique is desirable in order to permit many of these fractions to meet a pour point standard. In particular, many light gas oil fractions, that is, those which are used for No. 2 fuel (home heating oil) and/or Diesel fuel, have pour points which are too high to permit their intended use. A typical pour point specification is 0.degree. F., whereas it is not uncommon for such gas oil fractions to have untreated pour points of 50.degree. F. or higher.
Patents have issued on improved hydrodewaxing processes and catalysts, including U.S. Pat. No. 3,700,585 which discloses and claims such process using a ZSM-5 type zeolite catalyst.
Prior to the discovery in U.S. Pat. No. 3,700,585, reissued as Re. 28,398, the entire contents of both of which are incorporated herein by reference, a wide variety of zeolitic materials and particularly crystalline aluminosilicates had been successfully employed in various catalytic conversion processes. However, these prior art processes, in general, fell into one of two main categories. In one type of conversion process, a zeolite was employed which had a pore size sufficiently large to admit the vast majority of components normally found in a charge. These zeolites are called large pore size molecular sieves, and they generally have a pore size of from 6 to 13 Angstroms and are represented by zeolites X, Y and L. The other type of aluminosilicate was one which had a pore size of approximately 5 Angstrom units and it was utilized to preferentially act upon normal paraffins to the substantial exclusion of other molecular species. Thus, by way of oversimplification, up until that invention, there were only two types of aluminosilicates which were available for hydrocarbon processing--those which would admit only normal paraffins and those which would admit all components normally present in a hydrocarbon feed charge.
In the reissue patent U.S. Pat. No. Re. 28,398, there was disclosed and claimed, among other things, catalytic dewaxing of oils over zeolites having the characteristics X-ray diffraction pattern of zeolite ZSM-5 and the compositions: EQU (0.9.+-.0.2)M.sub.2/n O:Al.sub.2 O.sub.3 :(5-100)SiO.sub.2 :zH.sub.2 O
wherein M was a cation, n the valence thereof, and z was from 0 to 40. These compositions had SiO.sub.2 /Al.sub.2 O.sub.3 (silica/alumina) mole ratios of 5:1 to 100:1.